This invention is concerned with economically converting low BTU gas to high BTU gas. More particularly, methane is produced by reacting carbon monoxide separated from purified low BTU gas with hydrogen produced by the steam-iron process using the deoxidizing properties of the low BTU gas. This also removes nitrogen from the final product.
This disclosure relates to a process for producing methane from a low BTU gas containing hydrogen, carbon monoxide, nitrogen and relatively small amounts of the other materials found in the gas produced by the gasification of carbonaceous materials with air. This gaseous product is sometimes called producer gas. By way of example, a producer gas produced from the gasification of coal with air may contain on a dry basis 15% hydrogen, 29% carbon monoxide, 50% nitrogen, 5% carbon dioxide and 1% methane.
The shortage of natural gas, which is predominantly methane, has greatly increased the need for economic production of synthetic natural gas. Gasification of carbonaceous materials, for example coal, produces a low BTU gas generally having a fuel value below 300 BTU/std. ft.sup.3 which is too low for most natural gas uses. Methane has a heat of combustion of 1013 BTU/ft.sup.3. A large number of processes have been proposed for enhancing the heat value of low BTU gases. Many of these processes produce what is called an intermediate BTU gas because the final product is diluted with low heat value gases. Low BTU gases lack sufficient hydrogen. The economics of converting low BTU gases to methane is affected by the cost of hydrogen and process steps required to produce a good quality methane gas. This is affected by the purity of the various reaction streams and final product.
Accordingly, it is an object of this invention to provide a method of producing a high BTU product in a way that effectively uses the carbon monoxide in the feed gas and the remaining low BTU gas to reduce the cost of producing hydrogen in a way that produces a final pipeline product that requires no further treatment other than water removal.